Semiconductor

Q1 What are silicon wafers used for ?

Q2 What is "silicon" in the first place ?

Q3 Although silicon is the second most common element, I don't think I see it very often. Where can I find it ?

Q4 Is the "silicon" of silicon wafers different from "silicone" ?

Q5 What characteristics does a semiconductor have ?

Q6 Why is silicon the most common element for semiconductor devices ?

Q7 Are there some types in semiconductors ?

Q1 What are silicon wafers used for ?

A The goods using silicon wafers are actually very close to you, such as computers you are using right now, mobile phones, game machines, transistor radios, etc. From discrete or individual device with single function, such as diode and transistor, to an integrated circuit (IC) having a circuit of millions of discretes within an area of a few centimetres square, semiconductors are used in almost every electric devices around you, and most of semiconductors are made from silicon. Silicon wafers are used as substrates on which circuits of semiconductor devices are mounted.

Q2 What is "silicon" in the first place ?

A Silicon is the second most common element existing on the Earth, next to oxygen.

Q3 Although silicon is the second most common element, I don't think I see it very often. Where can I find it ?

A The main element of soils, sands, and stones around you is silicon. Silicon is, however, easily bonded with oxygen, so that it usually exists in the oxide form of SiO2. This SiO2 is called "silica stone".

Q4 Is the "silicon" of silicon wafers different from "silicone" ?

A Both "silicon" and "silicone" are made from the same silica stones. The "silicon" used in the semiconductor industry is almost pure silicon with the purity at 99.999999999 % (so-called "eleven nines") by chemically reducing and distilling silica. The "silicone", on the other hand, is a kind of synthetic plastics, in which silicon plays a main element of the material. So, although they are originated from the same material, "silicon" and "silicone" are totally different substances.

Q5 What characteristics does a semiconductor have ?

A There are three types of characteristics which materials conduct electric current: conductors such as metals conduct the current easily; insulators such as glass and rubbers do not conduct the current; and, semiconductors have intermediate resistivities between conductors and insulators. In addition to silicon, typical semiconductors include germanium (Ge) and gallium arsenide (GaAs).

Q6 Why is silicon the most common element for semiconductor devices ?

A There four main reasons: The resources are abundant. It can be easily refined up to a nearly perfect purity. It is easy to control the resistivity by single crystallisation, and addition of dopants. Stable oxide films enables easy processing of circuit integration.

Q7 Are there some types in semiconductors ?

A Although it is said above that semiconductors have intermediate resistivity between conductors and insulators, the elements called semiconductors themselves alone have almost the same characteristics as insulators. In order to make them conduct electric current, it is necessary to add a very small amount of metal elements (called dopant or impurity) during the single crystallisation process. Depending on this dopant, semiconductors are divided into two types, N (negative) type and P (positive) type. In the N type semiconductors, electrons are in excess. These excessive electrons, called free electrons, plays the role of conducting electric current. The P type semiconductors, on the other hand, are short of electrons, and have vacant sites of electrons called holes. The movement of electrons to fill such holes makes electric current